var dustObject=function () {
	this.x=[];
	this.y=[];
	this.amp=[];
	this.number=[];
    this.alpha;
}
dustObject.prototype.num=30;

dustObject.prototype.init=function () {
	
	for (i=0;i<this.num;i++) {
		this.x[i]=Math.random()*canWidth;
		this.y[i]=Math.random()*canHeight;
		this.amp[i]=20+Math.random()*15;
		this.number[i]=Math.floor(Math.random()*7);
	}
	this.alpha=0;
}
dustObject.prototype.draw=function () {
	this.alpha+=deltaTime*0.0008;
	var l=Math.sin(this.alpha);
	for (i=0;i<this.num;i++) {
		var no=this.number[i];
		context1.drawImage(dustPic[no],this.x[i]+this.amp[i]*l,this.y[i]);
	}
}